The invention relates to a magnetic field sensor that is axially adjustably arranged on the housing of a cylinder. Such magnetic field sensors (hereinafter frequently simply “sensor”) have been successfully employed for precisely determining the location of pistons, such as pneumatic or hydraulic pistons, inside a cylinder in a touchless manner. To achieve this, sensors can be axially moved and then fixed at a given position in guide grooves arranged on the outer surfaces of the cylinder housing.
The guide grooves can have a cylindrical as well as a rectangular cross-section, and longitudinal slits provide access to the grooves from the outside.
Such a mounting of magnetic field sensors on a cylinder is disclosed by German patent publication DE 44 35 675 A1. The sensor disclosed in that publication has an essentially circular cross-section and is placed in a longitudinally slitted cylindrical groove.
Sensors must be inserted into such a C-groove from the free end of the groove. Once in the groove, the sensor can be axially moved into the desired position. Removal of the sensor from the C-groove is only possible by pushing the sensor out of the free end of the groove. This approach to inserting or removing the sensor from the housing of a cylinder is particularly disadvantageous when several sensors are simultaneously arranged in the groove because in such an event the sensors must be serially pushed into or out of the groove. In view thereof, German patent publications DE 196 43 413 and DE 196 53-222 disclose magnetic field sensors which have a cross-section so that they can be inserted into the partially open guide groove at any desired location along the length thereof. The sensors have a cross-section with a first, narrow side that can be inserted into the groove. Thereafter the sensor is rotated about its longitudinal axis to retain it in the groove. A set screw fixes the sensor in place and, when tightened, the screw engages and is supported by the base of the groove while it presses the sensor against a shoulder formed at the opposite side of the groove cross-section. A disadvantage of the known sensor positioning arrangements is that they necessarily form an air gap between the sensor and the cylinder housing which is caused by the mechanical tolerances of the guide groove and the cross-section of the sensor. The deviations in the air gap influence the magnetic fields, which in turn can adversely affect the functioning and accuracy of the sensor. A further disadvantage is that by fixing the sensor with a set screw the sensor becomes mechanically stressed, which can lead to a bending of or even damage to the sensor.